It generates a call graph of the functions and methods in a PHP file, example shown below.
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It had been sitting, festering on my HD for a while, and I thought "Hey, maybe someone else might find this helpful" so I uploaded it to phpclasses.org
So blow me, not only do they find it useful - but they want me to support the damn thing too! And then I get nominated for an award! I had a quick look at the source code. OMG - it's a mess!
So a couple of late nights were spent cleaning it up until the API is at least usable.
You can get the (cleaned up, slightly) source code here